Abstract: A network for matching an electrical source of audio signals to a piezoceramic driver for a high frequency loudspeaker. The network consists of all of the elements of a bandpass filter network, but with the parallel combination of an inductor and a capacitor in the output stage of the filter replaced by an autotransformer or autoinductor which transforms the input impedance of the piezoceramic transducer into an equivalent parallel capacitance and resistance which, together with the inductance of the autotransformer, supply the load resistance for the filter and replace the capacitor and inductor omitted from the output stage of the bandpass network. An additional shunt resistor may be placed across the output of the autotransformer to obtain the desired effective load resistance at the input of the autotransformer.

Abstract: An acoustical transformer or "phasing plug" for coupling the sound from an annular diaphragm to the throat of a compression-type loudspeaker. The phasing plug in the invention has the general shape of a doubly-truncated cone with an annular surface located on the larger end of the truncated cone and positioned adjacent to the diaphragm. The conical surface of the cone has spaced radial slots or channels formed therein connecting the truncated surfaces of the cone. These channels form air passageways for propagation of sound waves. The walls of the slots or channels are tapered such that the cross-sectional areas of the channels increase from their inlet ends near the speaker diaphragm, towards the outlet ends, positioned at the throat of the horn. The phasing plug provides an improved impedance match between the output of the annular diaphragm and the input of the horn.

Abstract: The output of an audio power amplifier fed to a loudspeaker driver is sensed and when this output exceeds a predetermined level, a switch control circuit operates to place a current limiting device, such as a power resistor, in series with one of the driver feed lines, thereby reducing the power fed thereto. An indicator may also be provided to indicate when the overload condition exists. Operation is made more accurate and distortion minimized by employing separate sensing and power channels in the circuit, the first of these channels operating to sense the overload while the second of these channels utilizes a portion of the amplifier output for driving the switch control circuit for placing the power limiter in the speaker line. The sensing channel is designed to sense the average voltage of the amplifier output, thus providing control more directly responsive to power. The power channel is designed to use audio power from the amplifier output only occasionally, thus producing a minimum of distortion.

Abstract: A loudspeaker horn has a throat section with a rectangular cross section to which the driver unit is coupled. The throat section has substantially parallel side walls joined together by diverging top and bottom walls. The horn has a rectangular mouth which is formed by a bell section which runs between the throat section and the mouth with an angular divergence corresponding to the desired horn dispersion pattern. If the mouth is made square, equal horizontal and vertical low frequency directivity roll off can be provided. On the other hand, with the speaker of the present invention, various relative horizontal and vertical directivity control can be obtained with different aspect ratios for the mouth. The walls of the bell section may be additionally flared outwardly at a portion thereof near the mouth to provide improved midrange directivity control. The use of planar sides between the throat section and the mouth also makes for an improved directivity pattern.

Abstract: A transistor amplifier circuit is arranged in a differential amplifier incorporated into a power amplifier output circuit having approximately unity voltage gain and capable of feeding high current and power outputs to a load in response to high level voltage inputs from a signal source. This same signal source may be connected to drive a plurality of different output circuits simultaneously. A decoupling diode is provided in series with the emitter of each of the transistors of the differential amplifier, these diodes having a reverse breakdown voltage which is of the order of twice the peak input voltage and the supply voltage such that in the event that a short should appear in the load or in the power amplifier being driven, the diodes will act to effectively decouple the output of the signal source from the short circuit, thereby preventing the signal source output from being loaded down and, as a result, distorted.

Abstract: Apparatus and method for precisely adjusting the spacing between the phasing plug of a horn type loudspeaker driver and the diaphragm of such loudspeaker. The base of the pole piece is threaded and threadably engages a mating apertured portion of a back plate. A micrometer is employed to adjust the height of the phasing plug above the surface of the top back plate by rotating the phasing plug on its threads. In this manner, spacing between the phasing plug and the diaphragm can be precisely set for each assembly.

Abstract: An acoustical horn suitable for use in conjunction with an acoustical driver to form a loudspeaker has a first section between its throat and a predetermined point therealong which has a first exponential flare rate, and a second section between the predetermined point and the mouth which has a second flare rate. The flare rates are chosen to afford improved frequency response over a single section exponential horn with the same length, mouth area and throat area.

Abstract: A method and apparatus for determining the directivity index (DI) and directivity factor (Q) of a loudspeaker is described. A microphone is placed in the throat of a horn-type loudspeaker to measure the acoustical pressure at this point. A second microphone is placed along an extension of a central axis of a loudspeaker at a predetermined distance from the mouth of the loudspeaker to measure the acoustical pressure at this point. The output of each of the microphones is rectified and converted to decibel form. The decibel signal representing acoustical pressure at the throat is subtracted from the signal representing the measured pressure at the predetermined distance. A signal (in decibel form) representing the distance of the second microphone from the mouth of the horn is added to the difference signal and a signal (in decibel form) in accordance with the diameter of the loudspeaker throat is subtracted from the difference signal to provide a signal in accordance with directivity index.

Abstract: A modular printed circuit board assembly has a plurality of printed circuit boards each of which is integrated with a separate heat sink to form a modular unit. Each such modular unit is removably supported in a housing on a separate pair of support tracks in the base and top cover of the housing, bottom edges of the printed circuit board and a runner formed on the edge of the heat sink riding in these tracks. Each of the heat sinks has a flange portion to which the associated printed circuit board is attached and on which elements such as power transistors which generate a substantial amount of heat are directly mounted. The main body portion of each heat sink has a plurality of fins in the form of longitudinal strips with longitudinal slots being formed between the fins.

Abstract: A plurality of similar power amplifier circuits are connected in parallel in the output of an amplifier between the amplifier's voltage amplifier circuit and the load. Each of these amplifier circuits has a similar ballasting resistor connected between its output and the load. The amplifier circuits have unity closed loop voltage gain. The value of the ballasting resistors is empirically chosen such that these resistors are capable of accommodating differences in the outputs of the amplifier circuits which may occur, such that the load is equally shared between the amplifier circuits.

Abstract: An electronic filter circuit having controlled "Q" with variations in attenuation. A plurality of filter networks are connected in parallel between the output and the input of an amplifier in a manner such as to be capable of selectively providing negative feedback to the amplifier. Each filter network includes inductive, capacitive and resistive elements, with a potentiometer forming part of the resistance thereof. Each potentiometer is connected in series with a resistor having the same value thereas, the arm of the potentiometer being connected to its associated filter network such that the "cut" to which the potentiometer is set determines the total value of the resistance presented by the filter network in the feedback circuit. The potentiometers and associated resistors are each connected in series with each other, these series connected elements being connected in parallel between the input and the output of a unity gain amplifier.

Abstract: An acoustical transformer or "phasing plug" for coupling sound from a speaker diaphragm to the throat of a horn. The phasing plug of the invention is in the general shape of a dome on one side and a truncated cone on the other, and has evenly spaced radial slots or channels formed therein, these slots forming air passageways for propagation of the soundwaves. The walls of the slots are tapered exponentially from their inlet ends at the speaker diaphragm towards a flat plane outlet at the throat of the horn, to provide an optimum impedance match between the output of the diaphragm and the input of the horn; the sound channels formed by the slots exponentially increasing in area between their inlets and outlets. Transformation from a spherical wave front at the input to a plane wave front at the outlet is assured by the shaping of the channels to make the distances between corresponding points at the channel inlets and outlets equal to each other.

Abstract: The coil form for a loudspeaker voice coil is made of a material having high thermal conductivity. The coil form is attached to or integrally formed with a highly thermally conductive spider member which resiliently supports the coil form on the frame structure of the speaker, which also has high thermal conductivity. In one embodiment of the invention a heat sink member to facilitate the dissipation of the thermal energy is attached to the speaker frame structure. In an embodiment involving a horn type speaker, the horn element, which is made of a thermally conductive material, is attached to the speaker frame and also functions as a heat dissipator. In this manner, the likelihood of overheating of the speaker voice coil is greatly diminished.

Abstract: A power supply has both high and low voltage power sources connected to a common output terminal. A switching circuit is connected between the high voltage source and this terminal, the switching circuit being controlled by a control circuit. The control circuit operates in response to malfunction and temperature sensors when these sensors have outputs indicative of equipment operating conditions outside of predetermined ranges for each of the sensed parameters. When the control circuit is not being actuated by an output from one of the sensors, the switching circuit is actuated to connect the high voltage output to the output terminal. In the event, however, that one of the temperature or malfunction sensors senses a condition outside of range, the control circuit is actuated, thereby deactuating the switching circuit to remove the high voltage output from the output terminal, leaving low voltage output.

Abstract: A technique for accurately aligning the voice coil of a high frequency driver type loudspeaker in an annular magnetic gap formed between the top plate and the pole piece-phasing plug assembly thereof. A pair of dowels are attached to the top plate by means of screws, at positions separated from each other. The inside diameter of the dowels is greater than the diameter of the screws so as to permit radial adjustment of the position of the dowels on the screws. The screws are first left loose so that the dowels have limited freedom of radial movement. A jig member having a plurality of radial finger portions arranged in a circle is placed over the pole piece-phasing plug assembly with the ends of the finger portions lying in the magnetic gap against the side of the phasing plug.